The present invention relates to a fuel cell system and to a fuel-cell vehicle.
In a fuel-cell vehicle, the temperature of fuel cells rises due to an exothermic reaction of the fuel cells and thus, while the fuel cells are cooled by a coolant, a radiator installed in a cooling system radiates heat of the coolant to maintain the operating temperature of the fuel cells at an optimum value (for example, 80° C.).
The coolant of fuel cells flows through a fuel-cell stack and there is a danger of a short circuit of cells or a leakage of current if electrical conductivity of the coolant is high. Thus, ion exchanged water (whose electrical conductivity is 1 mS/m or less) or low-conductive antifreeze (whose electrical conductivity is, for example, 10 mS/m or less) is used as the coolant (JP 2000-208157 A, JP 2001-164244 A).
A fuel-cell vehicle is supposed to be used in an environment in which the temperature falls to zero or below and thus, the use of ion exchanged water, which may be frozen, is not preferable. Therefore, glycols often used as a freezing-point depressant of an antifreeze for vehicle are preferably used as a coolant of fuel cells. However, glycols are known to generate corrosive substances such as organic acids due to heat degradation and to corrode metal components. Thus, when glycols are used as a coolant, an inhibitor such as an anticorrosion agent and an antioxidant is typically added to the coolant (JP 2001-164244 A, WO 03/094271 A).
The coolant poses a problem that electrical conductivity of the coolant is high because of ionization of products of such organic acids or the like caused by heat degradation or elution of ions from component materials (such as rubber and metal) in the cooling system. Thus, electrical conductivity of the coolant is maintained low by installing an ion exchange resin in the cooling system of fuel cells to remove ions (JP 2002-172391 A, JP 2004-192959 A). A mixed bed ion exchange resin in which both a cation exchange resin and an anion exchange resin are mixed is used as the ion exchange resin (JP 2007-299574 A).